Senator Barbara Boxer (D., Calif.) wasn’t always a fan of comprehensive immigration reform. In 2007, as the Senate was debating the reform package backed by President George W. Bush, she warned that it would “exert downward pressure on wages at a time when we are already losing our middle class.”

She sponsored an amendment to eliminate the bill’s guest-worker program, which would have allowed about 600,000 unskilled workers into the country on temporary visas. The program, Boxer argued at the time, was designed “to create a permanent pool of insecure and low-paid workers whom I believe will never leave the country, even though they are supposed to, according to the rules of the program. This will only continue the cycle of illegal immigration.”

Boxer was not alone. Sixteen Democrats, including labor-union allies Sherrod Brown (Ohio) and Tom Harkin (Iowa), voted against the final bill that year, many after expressing similar concerns about its potential impact on American workers.

Fast forward to 2013, and those concerns have all but disappeared. On June 7, Boxer praised the “fair and effective guest-worker program” in the Gang of Eight legislation. The bill “will increase wages for workers,” she said. “I’m excited about it . . . It is so overdue.” And though Boxer said she would push for “amendments that are friendly to workers,” her support for the final package is all but guaranteed.

Notably, the AFL-CIO, which opposed the 2007 legislation, is backing the Gang of Eight, having struck a deal with Senator Chuck Schumer (D., N.Y.) and the Chamber of Commerce on the issue of guest workers. By signing on to the Gang’s proposal, the powerful union (with its supersized campaign war chest) has given most Democrats a green light to support it. A top Republican senator tells National Review Online he wouldn’t be surprised if every Democrat voted for the proposal, given the strong desire to pass it with at least 70 votes and put pressure on the GOP-controlled House.

Liberals might assume that, because Big Labor is backing the bill, American workers stand to benefit. A Congressional Budget Office analysis suggests otherwise. The bill would create an “influx” of low-skilled, low-wage temporary workers over the next several years, the CBO predicts, and, as a result, “the unemployment rate would be slightly higher than it otherwise would be and average wages would be slightly lower.”

Proponents of the bill will point out that, according to the CBO, average wages would stop declining in about 2024 and would increase over the following decade. Opponents, however, might wonder if there aren’t better ways to reform the immigration system, ones that don’t involve a decade’s worth of wage stagnation.

And if the CBO’s projections are accurate, why would labor unions be supporting the bill? It might have something to do with the fact that the union-membership rate rose to 12.1 percent in 2007, but has declined pretty steadily ever since, reaching 11.3 percent in 2012. Millions of new workers mean millions of potential dues-paying union members added to their ranks.

And liberals are willing to swallow their past criticisms in order to achieve other goals, such as legalization and eventual citizenship for illegal immigrants. “I think a number of Democrats sense that Republicans are nearing the point of self-immolation with this immigration bill,” a Republican aide tells NRO, “and are willing to sacrifice American workers in order to pass a bill that they believe will bring about the end of the Republican party.”

The CBO also said guest workers are likely to overstay their temporary visas, thus exacerbating the problem of illegal immigration, just as Boxer feared in 2007. But as National Review’s editors have pointed out, few lawmakers in either party have been willing to have a substantive discussion about many of the most important aspects of the bill. Democrats have been particularly silent.

Only Bernie Sanders, an avowed socialist from Vermont who caucuses with the Democrats, has shown any real consistency on the issue. He is concerned that the Gang of Eight’s “huge expansion in the guest-worker program” is unwise during a time of such high unemployment, particularly among the young and less educated. “We should not pass legislation which makes it harder for young people to get jobs in order to put away a few bucks to help pay for college,” Sanders said on the Senate floor Tuesday.

So, it may be that one of the few Democratic votes against the “bipartisan” immigration bill will come from a socialist. However, some Republicans believe Sanders’s criticism is mostly bluster. As one GOP aide puts it, “If they need him to vote yes, he’ll vote yes.”